Winter Warnings

By Robert N. Rossier, EAA 472091

This piece originally ran in Robert’s Stick and Rudder column in the February 2021 issue of EAA Sport Aviation magazine.

Most pilots understand, at least from a theoretical perspective, the dangers associated with icing. It accumulates on the airframe and various surfaces, adding weight and drag, and destroying lift. For an aircraft not properly equipped and pilot not properly trained, icing is a killer — one that acts quickly. That’s why we pay careful attention to known icing conditions and stay away from the danger zone.

Unfortunately, structural airframe icing isn’t the only form of ice with which we contend. Frigid temperatures can cause ice to form in other ways and places. These “ice follies” have a nasty habit of snaring unwary pilots.

On many a chill morning, we might find our aircraft wearing a furry coat of frost. Perhaps it covers the wings, the control surfaces, and the windscreen. At first glance, it might not appear to be a significant hazard, but research has shown that even modest amounts of frost can reduce lift by 40 percent. In days past, it was considered acceptable to merely polish the frost, but it turns out that this practice does not always eliminate the danger. The only real way to ensure safe flight is to remove that frost. The best methods are to place the aircraft in a heated hangar or park the aircraft in the sun and let nature do the rest. Either way, it’s a really good idea to remove any remaining moisture with a towel so it doesn’t refreeze and cause new problems.

Another cold weather hazard we might not readily notice is that ice can form in unseen locations and cause serious, life-threatening problems. As someone who has lived and flown mostly in regions where subfreezing temperatures dominate for a lengthy portion of the year, I have personally experienced some of the less obvious forms of ice-generated flight hazards. If the weather is cold enough, moisture trapped in a cable such as a throttle or propeller control can remain undetected while on the ground but then freeze solid when subjected to the in-flight blast of air and lower temperatures of flight. A frozen prop or throttle control in cruise provides a unique opportunity for a pilot to exercise his or her troubleshooting capacity, but perhaps such scenarios are better explored in a hangar flying session than in flight.

Another way the cold can snag us is through moisture trapped in a brake line. In this scenario, the moisture can freeze, creating a plug in the brake line that either locks a brake or prevents it from engaging. Either way, it can be a problem, unless we like the idea of movement in tight circles on the ground. Not funny!

Perhaps more frightening is a scenario that occurred at a flight school in the Denver area. In this case, snow or ice had melted and water found its way into the interior of an aileron, where it subsequently froze. It wasn’t anything that a pilot would necessarily notice on a preflight, but the pilot knew he had a problem when ailerons began to flutter in flight due to the imbalance condition. He slowed down and landed safely, but it could have gone differently. In theory, that could have resulted in a flight control separating from the aircraft in flight — not exactly the type of experience any of us are looking for. Perhaps a good set of wing covers would prevent such an occurrence to start with.

A similar situation occurred after a few days when light snow and ice accumulated with intervening thaw-freeze cycles. This time the meltwater collected inside the propeller spinner and then froze solid. During run-up, the pilot noticed a rather violent vibration due to the imbalance and taxied back to the ramp to have the problem checked out. A mechanic figured out what the problem was, removed the spinner, and brought it inside to remove the ice. It turns out the aircraft had been parked with the propeller at an angle that allowed meltwater to run down the propeller blade and collect in the spinner. Leaving the propeller in a horizontal position might help prevent meltwater from a propeller blade from draining into the spinner. It’s an easily overlooked detail, but it can be an important one.

Yet another hazard of winter weather is water in the fuel, which can freeze and form a plug that prevents fuel flow. Even tiny ice crystals suspended in the fuel can collect and restrict fuel flow. It doesn’t take much imagination to see where such a situation might take us.

While leaving an aircraft parked in a heated hangar has clear advantages in avoiding some of the pitfalls of winter flying, it can also result in unintended consequences. Several years back, I read an accident report involving the pilot of an amphibious aircraft who experienced a harrowing situation while in cruise flight in cold conditions. Water had collected against a bulkhead, forming a sort of “puddle” through which the elevator control cables passed. In the freezing conditions at high altitude, the water froze and jammed the elevator control cables in place. Imagine this pilot, flying along in cruise, when he suddenly realizes the elevator control is stuck and refuses to move. Perhaps using the trim tab (operating in reverse) would be one way to manage the crisis, but it isn’t a situation where the odds are in our favor.

Those who fly in cold environments know the importance of preheating the engine, but we don’t always think to preheat the cockpit as well. Especially when it is really cold, gyroscopic instruments may have problems since the lubricant on their bearings can become ineffective and prevent the gyros from spinning up and operating properly. Ice can also form on the interior of the windscreen, in the headliner, and in other locations in the cockpit. When it melts, the drops can rain down and find their way into important things, like electronics in the instrument panel, which is not where we would like them to go. Some pilots get around this by placing a towel over the glare shield to catch any drops that fall during the cockpit preheating process. It’s not a bad idea.

An instructor friend of mine had an exciting experience years ago when flying with a student on a somewhat slushy runway. What happened was the slush splashed up under the wheelpants during the takeoff and landing roll, and then froze solid once the aircraft was airborne. The net effect was locking the brake on one side of the aircraft, which made the subsequent landing a bit more exciting than normal. Fortunately, nobody was injured, but it did cause a flat tire that nearly sent the aircraft and its occupants on an unplanned off-runway excursion. We might want to consider removing the wheelpants for the winter to help prevent such a scenario.

Winter does have its challenges, many of which can result in a particularly bad day of flying. If we spend at least some time reflecting on the many ways that ice can create an unrecognized hazard, we might be more likely to take actions that prevent such situations. On the other hand, some days it’s just better to stay home and drink some hot cocoa.

Robert N. Rossier, EAA 472091, has been flying for more than 30 years and has worked as a flight instructor, commercial pilot, chief pilot, and FAA flight check airman.

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